Thermoplastic molding materials

ABSTRACT

Thermoplastic molding materials contain a blend of a polyphenylene ether with a copolymer which consists of monovinyl-aromatic monomers, alkyl acrylates where alkyl is of not more than 8 carbon atoms and, if required, an elastomer component having a glass transition temperature of ≦0° C.

The present invention relates to thermoplastic molding materials which are based on polyphenylene ethers and styrene/methyl methacrylate copolymers and may or may not have been toughened.

Blends of polyphenylene ethers and styrene polymers are known, and have been described in a number of patents. The relevant prior art includes (1) U.S. Pat. No. 3,383,435, (2) German Laid-Open Application DOS No. 2,713,430, (3) U.S. Pat. No. 4,360,618, (4) European Pat. No. 55,473 and (5) German Laid-Open Application DOS No. 3,127,233.

(1) describes compositions comprising polyphenylene ethers and styrene resins. Either the latter can be modified with rubber, generally polybutadiene, or pure polystyrene can be used. However, the heat resistance and the mechanical properties of these blends, and their resistance to chemicals, frequently do not meet the requirements set.

If the styrene resin in (1) is replaced by styrene/maleic anhydride copolymers (S-MAA), as described in (2), the heat distortion resistance of the blends, and their resistance to chemicals, can be improved, but the mechanical properties of the blends obtained are unsatisfactory.

(3) describes blends of polyphenylene ethers and styrene/acrylonitrile copolymers which possess high rigidity and very good resistance to chemicals. However, the toughness and the heat distortion resistance are not completely satisfactory.

Blends of polyphenylene ethers and copolymers of olefins and glycidyl acrylates or methacrylates are described in (4). The addition of this copolymer improves the processability of these blends, but the heat distortion resistance and the rigidity are reduced.

Finally, (5) describes blends of polyphenylene ethers, an EPDM polymer, high-impact polystyrene and a styrene/butyl acrylate copolymer consisting essentially of a polybutyl acrylate base polymer onto which polystyrene has been grafted. Such blends possess good weather resistance as well as good toughness and processability, but the heat distortion resistance, the rigidity and the resistance to chemicals are unsatisfactory.

It is an object of the present invention to provide thermoplastic molding materials which are based on blends of polyphenylene ethers and styrene polymers and which possess sufficiently high heat distortion resistance coupled with good resistance to chemicals and well balanced mechanical properties.

We have found that this object is achieved, in accordance with the invention, by molding materials which contain a mixture of

(I) from 95 to 5% by weight of a polyphenylene ether and

(II) from 5 to 95% by weight of a copolymer consisting of

(A₁) from 74 to 99 parts by weight of a monovinyl-aromatic monomer,

(A₂) from 1 to 26 parts by weight of an alkyl acrylate where alkyl is of not more than 8 carbon atoms, and

(III) from 0 to 20 parts by weight of an elastomer component which has a glass transition temperature of ≦0° C., the sum of the number of parts by weight being 100 when totaled with the parts by weight of (A₁) and (A₂).

The components of the novel molding material, their preparation, and the preparation of the molding material are described below.

COMPONENT I

Component I of the novel molding material comprises one or more resins which are composed of a polyphenylene ether (PPE) and are present in amounts of from 95 to 5, preferably from 70 to 30, % by weight, based on the mixture of I and II.

The polyethers are compounds which are based on polyphenylene oxides disubstituted in the ortho-position, the ether oxygen of one unit being bonded to the benzene nucleus of the adjacent unit. Not less then 50 units should be bonded to one another in this way. The polyethers can carry, in the ortho-position to the oxygen, hydrogen, halogen, a hydrocarbon radical which does not possess a tertiary α-hydrogen atom, a halohydrocarbon, phenyl or a hydrocarbon-oxy radical. Examples are poly(2,6-dichloro-1,4-phenylene)ether, poly(2,6-diphenyl-1,4-phenylene)ether, poly(2,6-dimethoxy-1,4-phenylene)ether, poly(2,6-dimethyl-1,4-phenylene)ether and poly(2,6-dibromo-1,4-phenylene)ether. Poly(2,6-dimethyl-1,4-phenylene)ethers are preferably employed, those having an intrinsic viscosiy of from 0.45 to 0.65 dl/g (measured in chloroform at 30° C.) being particularly preferred.

The polyphenylene ethers can be prepared from the phenols in a conventional manner, for example in the presence of a complex-forming agent, such as copper bromide or sec.-dibutylamine.

COMPONENT II

Component II of the novel molding materials is a styrene/alkyl acrylate copolymer which may or may not have been toughened and which consists of components (A₁) and (A₂).

The novel molding materials contain component II in an amount of from 5 to 95, preferably from 30 to 70, % by weight based on the mixture of I and II.

The composition of component II is as follows:

Suitable monovinyl-aromatic monomers (A₁) are styrene, α-methylstyrene and styrenes of not more than 12 carbon atoms which are alkylated in the nucleus, particularly preferably styrene, α-methylstyrene and paramethylstyrene.

Suitable monomers (A₂) are alkyl acrylates where alkyl is of not more than 8 carbon atoms. Methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acryate, isobutyl acrylate, tert.-butyl acrylate, ethylhexyl acrylate and hydroxypropyl acrylate are preferably employed, and methyl acrylate, ethyl acrylate, butyl acrylate and ethylhexyl acrylate are very particularly preferred.

Component II contains from 74 to 99, preferably from 75 to 99, parts by weight of (A₁) and from 1 to 26, preferably from 1 to 25, parts by weight of (A₂), the sum of the number of parts by weight being 100, unless component III is present.

The constituents of component II are prepared by continuous copolymerization of the monomers (A₁) and (A₂) at elevated temperatures, while stirring vigorously. The monomers (A₁) and (A₂) are introduced continuously into a polymerization vessel, and an amount of polymerization mixture equivalent to these amounts is simultaneously removed from the vessel (cf. A. W. Hanson and R. L. Zimmermann, Industrial Eng. Chemistry 49 (1957), 803). However, the constituents A₁ and A₂ can also be polymerized by any other conventional polymerization method.

Component III is an elastomer component which may or may not be present in the novel molding materials. It is a graft polymer which is present in an amount of from 0 to 20, in particular from 1 to 18, parts by weight, the sum of the number of parts by weight of component III, (A₁) and (A₂) being 100.

This graft copolymer consists of from 10 to 50, preferably from 15 to 45, parts by weight of a mixture of one or more vinyl-aromatic monomers of not more than 12 carbon atoms, and from 0.1 to 25, preferably from 5 to 20, parts by weight of one or more (meth)acrylates and/or acrylonitrile and/or (meth)acrylic acid and/or maleic anhydride as a grafted shell, on 50-90, in particular 60-80, parts by weight of an elastomeric grafting base (rubber component).

This rubber component should have a glass transition temperature (according to K. H. Illers and H. Breuer, Kolloid-Zeitschrift 176 (1961), 110) of below 0° C. Examples of suitable rubbers are polybutadiene (cf. German Laid-Open Applications DOS No. 1,420,775 and DOS No. 1,495,089), copolymers of butadiene and styrene (cf. British Pat. No. 649,166), copolymers of butadiene and styrene and polyacrylates which may or may not be crosslinked (cf. German Published Applications DAS No. 1,138,921, DAS No. 1,224,486 and DAS No. 1,260,135), copolymers of acrylates and butadiene (cf. German Published Application DAS No. 1,238,207), elastomers of copolymers of acrylates with styrene, acrylonitrile and vinyl ethers and copolymers of ethylene with a non-conjugated diene (EPDM rubber), and hydrogenated styrene/butadiene rubber polymers.

The vinyl-aromatic graft monomers are styrene, α-methylstyrene and/or styrenes of not more than 12 carbon atoms which are alkylated in the nucleus; suitable polar monomers are acrylates and methacrylates of alkanols of not more than 8 carbon atoms, acrylonitrile, acrylic acid, methacrylic acid and maleic anhydride, and mixtures of these.

The preparation of the graft copolymers is known per se. They can be prepared by, for example, polymerization of a mixture of styrene and (meth)acrylates in the presence of a rubber.

The graft copolymerization can be carried out in a conventional manner, in solution, in suspension or, preferably, in emulsion.

It is essential for success that the constituents of components II and III of the novel molding material have a composition, and are matched up with one another in the mixture, so that the absolute amounts of the polar monomers present in each differ by less than 10.

Components II and III are combined into a single composition, preferably by mixing melts of their constituents. To do this, the constituents, in the form of melts, are mixed at from 200° to 260° C. in an extruder, a roll mill or a kneader, the residence time being a few minutes. However, it is also possible to mix solutions of the constituents and then to volatilize the solvents.

In addition to containing the afore-described components the novel molding material can, if required, contain effective amounts of conventional additives. Examples of such additives are pigments, dyes, fillers, flameproofing agents, such as triaryl phosphates, other compatible polymers, antistatic agents, antioxidants and lubricants.

PREPARATION OF THE NOVEL MOLDING MATERIALS FROM COMPONENTS I, II AND III

The molding material according to the invention can be prepared as described below. However, the molding material is preferably prepared from constituents of components I, II and III, with or without other additives, by mixing the soft and hard constituents (of components II and III) and the polyphenylene ether. The preparation is usually carried out in an apparatus which permits homogeneous mixing, eg. a kneader, an extruder or a roll mill.

However, it is also possible to prepare the novel molding material by thoroughly mixing solutions of the individual components and then evaporating the solvent. Combined processes in which solutions and melts are mixed, for example in a devolatilization extruder, have also been successfully tested.

The copolymers A₁ to A₅ listed in Table 1, and where relevant the graft rubbers B₁ and B₃ stated in Table 2, were used for the preparation of the novel molding materials. Composition and other properties are shown in the stated tables.

A commercial product based on poly(2,6-dimethyl-1,4-phenylene)ether and having an limiting viscosity of 0.5 [dl/g] and a notched impact strength of 4 (kJ/m) was used as component I.

                  TABLE 1                                                          ______________________________________                                         Styrene/alkyl acrylate copolymers (constituent A)                              Composition in parts                                                                             Notched impact                                                                             Vicat                                            by weight         strength    temperature                                      Name  S      MA     EA   BA   (kJ/m.sup.2)                                                                             (°C.)                           ______________________________________                                         A.sub.1                                                                              80     20     --   --   4         99                                     A.sub.2                                                                              75     25     --   --   4         99                                     A.sub.3                                                                              73     27     --   --   4         99                                     A.sub.4                                                                              75     --     25   --   4         98                                     A.sub.5                                                                              75     --     --   25   5         90                                     ______________________________________                                          S = styrene,                                                                   MA = methyl acrylate,                                                          EA = ethyl acrylate and                                                        BA = nbutyl acrylate.                                                    

The copolymers A₁ to A₅ had a viscosity number of 75 (ml/g), measured on a 0.5% strength solution in dimethylformamide at 25° C.

For purposes of comparison, a graft copolymer (B₄) of styrene on polybutyl acrylate, as described in (5) was also prepared (cf. Table 2). The amount of grafted polystyrene was 30% by weight.

                  TABLE 2                                                          ______________________________________                                         Graft copolymers (component III)                                               Composition of Composition of the                                                                            Glass transi-                                    the rubber (%) grafted shell (%)                                                                             tion tempera-                                    Name  Bu       BA      S    MMA   AN    ture (°C.)                      ______________________________________                                         B.sub.1                                                                              100      --      80   20    --    -81                                    B.sub.2                                                                              --       100     80   20    --    -46                                    B.sub.3                                                                               50       50     80   15    5     -67                                    B.sub.4                                                                              --       100     100  --    --    -48                                    ______________________________________                                          Bu = butadiene,                                                                BA = nbutyl acrylate,                                                          S = styrene,                                                                   MMA = methyl methacrylate and                                                  AN = acrylonitrile.                                                      

Triphenyl phosphate was employed as component III.

The parameters stated in the experiments and comparative experiments were determined as follows:

1. The notched impact strength in (kJ/m²) was measured according to DIN No. 53,453, at a material temperature of 250° C., on injection molded standard small bars.

2. The modulus of elasticity in (N/mm²) was determined according to DIN No. 53,457, on injection molded dumbbell test pieces.

3.

(a) The viscosity numbers, VZ, in (ml/g) were determined for a 0.5% strength solution in dimethylformamide.

(b) The limiting viscosity ηsp/c in [cm³ /g] was measured in CHCl₃ at 30° C.

4. The Vicat softening point in °C. was determined according to DIN No. 53,460, method B, in silicone oil.

5. The glass transition temperatures of the rubbers were determined in accordance with K. H. Illers and H. Breuer, Kolloid-Zeitschrift, loc. cit.

6. The resistance to chemicals was checked and visually assessed in a short-time test with injection molded boxes which were filled with isopropanol and stored for 48 hours.

Rating:

1=no change

2=roughening of surface, cloudiness

3=deformation

The examples and comparative experiments which follow illustrate the invention. Parts and percentages are by weight, unless stated otherwise.

EXAMPLES 1 TO 9 AND COMPARATIVE EXAMPLES I TO IV

The components A_(n), B_(n) and III stated in Table 3 were premixed in a fluid mixer and then kneaded thoroughly in a Ko-kneader at about 220°-230° C., under nitrogen. The residence time was about 4 minutes. The granules obtained were melted in a single-screw extruder, the melt was extruded and the extrudates were face-cut to give uniform granules suitable for injection molding. Table 3 lists the properties of the mixtures.

As can be seen from the results shown in Table 3, blends possessing good mechanical properties can be obtained only in the case of random styrene/alkyl acrylate copolymers having a certain composition. Styrene/alkyl acrylate graft copolymers do not possess these advantageous properties, and this is attributable to incompatibility with the polyphenylene ether component of the mixture.

                                      TABLE 3                                      __________________________________________________________________________     Composition (% by weight)                                                                         Notched impact                                                                         Vicat  Modulus of                                                                           Resistance                             Components         strength                                                                               temperature                                                                           elasticity                                                                           to chemicals                           Example                                                                             I    II  III  (kJ/m.sup.2)                                                                           (°C.)                                                                          (N/mm.sup.2)                                                                         Rating                                 __________________________________________________________________________     1    70   30  --   7       157    3000  1                                      (100 parts of A.sub.1)                                                         2    70   30  --   7       157    3000  1                                      (100 parts of A.sub.2)                                                         3    70   30  --   7       156    2900  1                                      (100 parts of A.sub.4)                                                         4    70   30  --   8       150    2700  1                                      (100 parts of A.sub.5)                                                         6    60   40  --   13      146    2700  1                                      (74 parts of A.sub.2)                                                          (25 parts of B.sub.1)                                                          6    60   40  --   13      145     2600 1                                      (75 parts of A.sub.4)                                                          (25 parts of B.sub.3)                                                          7    60   40  --   14      140    2500  1                                      (75 parts of A.sub.5)                                                          (25 parts of B.sub.2)                                                          8    50   40  10   15      124    2400  1                                      (75 parts of A.sub.5)                                                          (25 parts of B.sub.2)                                                          9    50   40  10   16      121    2300  1                                      (50 parts of A.sub.4)                                                          (50 parts of B.sub.2)                                                          Comparative examples (not according to the invention)                          I    70   30  --   5       143    3000  2                                      (100 parts of A.sub.3)                                                         II   70   30  --   7       138    2700  2                                      (100 parts of B.sub.4)                                                         III  60   40  --   8       127    2600  3                                      (75 parts of A.sub.3)                                                          (25 parts of B.sub.3)                                                          IV   60   40  --   6       123    2600  3                                      (75 parts of B.sub.4)                                                          (25 parts of B.sub.1)                                                          __________________________________________________________________________ 

We claim:
 1. A thermoplastic molding material which contains a mixture of(I) from 95 to 50% by weight of a polyphenylene ether and (II) from 5 to 50% by weight of a copolymer consisting of(A₁) from 74 to 99 parts by weight of a monovinyl-aromatic monomer, (A₂) from 1 to 26 parts by weight of an alkyl acrylate where alkyl is of not more than 8 carbon atoms, and (III) from 0 to 20 parts by weight of a diene elastomer component which has a glass transition temperature of ≦0° C., the sum of the number of parts by weight of said elastomer when totaled with those of A₁ and A₂ being
 100. 2. A thermoplastic molding material as claimed in claim 1, wherein a homopolymer and/or a copolymer of 2,6-dimethylphenol are employed as the polyphenylene ether I.
 3. A thermoplastic molding material as claimed in claim 1, wherein the copolymer II is selected from the group consisting of styrene/butyl acrylate and styrene/ethylhexyl acrylate.
 4. A thermoplastic molding material as claimed in claim 1, wherein components I and II are employed in a ratio of 50-70% to 50-30%.
 5. A thermoplastic molding material as claimed in claim 1, which contains a triaryl phosphate.
 6. A thermoplastic molding material according to claim 1, wherein said elastomer component III consists of from 10 to 50 parts by weight of a graft copolymer as a grafted shell on 50 to 90 parts by weight of an elastomeric grafting base.
 7. The thermoplastic molding material of claim 6, wherein said graft copolymer contains one or more vinyl-aromatic monomers of not more than 12 carbon atoms and one or more monomers selected from the group consisting of acrylates and methacrylates of alkanols having not more than 8 carbon atoms, acrylonitrile, acrylic acid, methacrylic acid and maleic anhydride. 